Electrosurgical devices configured for use with a dry tip use electrical energy, often radio frequency (RF) energy, to cut tissue or to cauterize blood vessels. During use, a voltage gradient is created at the tip of the device, thereby inducing current flow and related heat generation in the tissue. With sufficiently high levels of electrical power, the heat generated is sufficient to cut the tissue and, advantageously, to stop the bleeding from severed blood vessels.
Current dry tip electrosurgical devices can cause the temperature of tissue being treated to rise significantly higher than 100° C., resulting in tissue desiccation, tissue sticking to the electrodes, tissue perforation, char formation and smoke generation. Desiccation occurs when tissue temperature exceeds 100° C. and all of the intracellular water boils away, leaving the tissue extremely dry and much less electrically conductive. Peak temperatures of target tissue as a result of dry RF treatment can be as high as 320° C., and such high temperatures can be transmitted to adjacent tissue via thermal diffusion. Consequently, this may result in undesirable desiccation and thermal damage to the adjacent tissue.
The use of saline inhibits undesirable effects such as tissue desiccation, electrode sticking, smoke production and char formation. However, an uncontrolled or abundant flow rate of saline can provide too much electrical dispersion and cooling at the electrode/tissue interface. This reduces the temperature of the target tissue being treated, and, in turn, can result in longer treatment time to achieve the desired tissue temperature for treatment of the tissue. Long treatment times are undesirable for surgeons since it is in the best interest of the patient, physician and hospital, to perform surgical procedures as quickly as possible.
RF power delivered to tissue can be less than optimal when using general-purpose generators. Most general-purpose RF generators have modes for different waveforms (e.g., cut, coagulation, or blend) and device types (e.g., monopolar, bipolar), as well as power levels that can be set in watts. However, once these settings are chosen, the actual power delivered to tissue and associated heat generated can vary dramatically over time as tissue impedance changes during the course of RF treatment. This is because the power delivered by most generators is a function of tissue impedance, with the power ramping down as impedance either decreases toward zero or increases significantly to several thousand ohms. Current dry tip electrosurgical devices are not configured to address a change in power provided by the generator as tissue impedance changes or the associated effect on tissue, and rely on the surgeon's expertise to overcome this limitation.